1. Description of Related Art
In an electrical installation system on a vehicle, when electrical loads, such as a power window, has any malfunction or when a wire harness composed of a plurality of electrical wires connecting a battery with respective loads has any trouble, the system generally operates to melt a fuse for great current interposed between the battery and the wire harness. As a result, the connection between the battery and the wire harness is broken to prevent respective loads, wire harness, etc. from being damaged.
In the above-mentioned electrical installation system, however, the great current fuse does not melt unless the current in excess of a predetermined allowable value flows through the fuse in spite of the occurrence of the above abnormalities. Therefore, there are a variety of protecting devices under development, which can detect the continuous flowing of a large current close to the allowable value and further break the connection between the battery and the wire harness.
In these protecting devices, FIG. 1 is a longitudinal sectional view showing one protecting device using a bimetal. The shown protecting device is made of insulating resin and others and comprises the following elements: a housing 103 provided, on its upper side, with a fuse container 102; a lid 113 closing the fuse container 102 of the housing 103; a power terminal 105 disposed in the lower side of the housing 103 and having its upper end projecting into the container 102 and the exposed lower end connected to a positive (+) terminal of a battery 104; a load terminal 109 also disposed in the lower side of the housing 103 and having its upper end projecting into the container 102 and the exposed lower end connected to a load 108 through a wire 107 forming a wire harness 106; a soluble member 110 constituted by low-melting point metals in the container 102 and having one end connected to the upper end of the power terminal 105 and the other end connected to the upper end of the load terminal 109; an intermediate terminal 111 disposed in the lower side of the housing 103 to take a middle position between the power terminal 105 and the load terminal 109 and having the terminal's exposed lower end connected to a negative (-) terminal of the battery 104; and a bimetal 112 formed to be a long plate member consisting of two different glued metals and also having a lower end connected to the upper end of the intermediate terminal 111 and the upper end bent in a L-shaped manner to face the soluble member 110.
Under condition that the current flows in order of the positive terminal of the battery 104, the power terminal 105, the soluble member 110, the load terminal 109, the wire 107 of the wire harness 106, the load 108 and the negative terminal of the battery 104 upon the manipulation of an ignition switch of the vehicle etc., when any trouble arises in either the load 108 or the wire harness 106 connecting the load 108 with the protection device 101 so that the current exceeding the allowable value flows through the soluble member 110, it is heated and molten off to protect the load 108 and the wire harness 106.
Alternatively, even when the current does not exceed the allowable value despite a great current flowing through the soluble member 110 due to any abnormality in either the load 108 or the wire harness 106 connecting the load 108 with the protection device 101, the soluble member 110 is still heated by the current flowing therethrough, so that the bimetal 112 begins to be deformed. At a point of time when a predetermined period has passed since the great current began to flow through the soluble member 110, the tip of the bimetal 112 finally comes into contact with the soluble member 110, so that a large short-circuit current flows through the soluble member 110 in the following order of the positive terminal of the battery 104, the power terminal 105, the soluble member 110, the load terminal 109, the wire 107 of the wire harness 106, the load 108 and the negative terminal of the battery 104 and finally, the soluble member 110 is broken off in heat.
In this way, even when the current less than the allowable value continues to flow in excess of the predetermined period, the circuit is broken off thereby to protect the wire harness 106 and the load 108.
Besides the above protecting device 101, another protecting device 121 shown in FIG. 2 has been under development.
The shown protecting device 121 includes the following elements: a housing 122 made of insulating resin or the like; a power terminal 124 embedded in one side of the housing 122 and having the terminal's lower end connected to a positive (+) terminal of a battery 123; a load terminal 128 also embedded in the other side of the housing 122 and having the terminal's lower end connected to a load 127 through a wire 126 forming a wire harness 125; a wire 131 consisting of an U-shaped soluble lead 129 of low-melting point metals etc. and a heat resistant cover 130 covering the lead 129, and also having one end connected to the upper end of the power terminal 124 and the other end connected to the upper end of the load terminal 128; a coil 132 of shape-memory alloy, which is previously memorized in its shape so as to wind around the wire 131 when the coil 132 is in the phase of martensite, whereas fasten the wire 131 in the mother phase when heated up to 120-170.degree. C.; and an exterior terminal 133 arranged outside the housing 122 and having the terminal's upper end connected to one end of the coil 133 and the other end connected to a negative (-) terminal of a battery 123.
Under condition that the current flows in order of the positive terminal of the battery 123, the power terminal 124, the soluble lead 129 of the wire 131, the load terminal 128, the wire 126 of the wire harness 125, the load 127 and the negative terminal of the battery 123 as a result of manipulating the ignition switch etc. and if any trouble arises in either the load 127 or the wire harness 125 connecting the load 127 with the protection device 121 so that the current exceeding the allowable value flows through the soluble lead 129, then it is heated and molten off to protect the load 127 and the wire harness 125 etc.
Alternatively, even if the current does not exceed the allowable value despite a great current flowing through the soluble lead 129 due to any abnormality in either the load 127 or the wire harness 125 connecting the load 127 with the protection device 121, the soluble lead 129 is still heated by the current flowing therethrough, so that the temperature of the coil 132 rises. When the temperature of the coil 132 reaches 120-170.degree. C. as a result of passage of a predetermined period since the great current began to flow through the soluble lead 129, the coil 132 transfers from the martensite phase to the mother phase and encroaches on the heat resistant covert 130 being softened by heat. As a result, the coil 132 comes into electrical contact with the soluble lead 129, so that a large short-circuit current flows through the soluble member 110 in the sequent course of the positive terminal of the battery 123, the power terminal 124, the soluble lead 129, the coil 132, the exterior terminal 133 and the negative terminal of the battery 123 and finally, the soluble lead 129 is broken off in heat.
In this way, even when the current less than the allowable value continues to flow in excess of the predetermined period, the circuit is broken off to protect the wire harness 125 and the load 127.
Nevertheless, the above-mentioned protecting devices 101, 121 still have problems as follows.
First, in the former protecting device 101 of FIG. 1, when the magnitude of current flowing the soluble member 110 changes, the bimetal 112 is deformed to change a period required to cut off the circuit due to the structure of the bimetal 112 where two kinds of metals of different rates of thermal expansion are glued each other.
Therefore, if there is caused a malfunction that an excessive current flows discontinuously, the temperature of the soluble member 110 does not rise in excess of a certain degree any longer, so that the wire harness 106, the load 108, etc. may be subjected to thermal damage before the protecting device 101 serves to cut off the circuit.
While, since it is detected whether an excessive current flows through the soluble lead 129 by the coil 132 of shape-memory alloy in the latter protecting device 121 of FIG. 2, when the magnitude of current flowing the soluble lead 129 changes, the coil 132 is deformed to change a period required to cut off the circuit.
Therefore, if there is caused a malfunction that the excessive current flows discontinuously, the temperature of the soluble lead 129 does not rise in excess of a certain degree any longer, so that the wire harness 125, the load 127, etc. may be heated excessively before the protecting device 121 serves to cut off the circuit.
Further, the bimetal and the shape-memory alloy coil are commonly characterized by their relatively-low deformation starting points (approx. 100.degree. C.), these elements are unsuitable to be used in a temperature range from 120 to 125.degree. C. corresponding to a temperature situation where the vehicle is in general use.
In the protecting devices of FIGS. 1 and 2, the bimetal 112 and the coil 132 (as heat-deformable and conductive members) commonly have variable heat-reactive periods influenced by the magnitude of currents. Additionally, these protecting devices have a common drawback that the heat-deformable and conductive members cannot operate at the occurrence of abnormality (excessive current) timely.
Besides the above-mentioned devices, there is a circuit breaking device under development, which comprises a pair of connecting terminals (one for battery; the other for load) and a conductive member in electrical contact with the above connecting terminals. In operation, when the vehicle has an abnormality, the conductive member is broken or shifted to cut off the electrical connection between the connecting terminal for battery and the connecting terminal for load, thereby breaking the circuit.
In this circuit breaking device under development, the connecting terminals are joined to the conductive member by means of soldering. Furthermore, the connecting terminal for battery is fixed to a wire for battery through a fastened screw etc., while the connecting terminal for load is also fixed to a wire for load through a fastened screw etc.
In the above-mentioned circuit breaking device, however, an inferior soldering sometimes arises from the screw-fastening in fixing the respective connecting terminals with the wires since an external stress is transmitted from each connecting terminal to the joint (soldering) part. Consequently, there is a problem of defective connection between the connecting terminals and the conductive member.
2. Field of the Invention
The present invention relates to a conductive connecting terminal to be joined to a conductive member, such as a thermit case, through a material of low melting point. Further, the invention also relates to a circuit breaking device with the above connecting terminal, which can break an electric circuit in a short time.